Operation of the gas-puff imaging diagnostic in the RFX-mod device

The reversed field pinch device RFX-mod (R=2m, a=0.5m) has started plasma experiments late in 2004. During the first year of operation a gas-puff imaging diagnostic has been used consisting of 32 optical lines of sight measuring radiation emitted from puffed gas on a plane normal to the local magnetic field. Such diagnostic system allows the investigation of the edge plasma properties with high time resolution even at high plasma currents (greater than 1MA). In the present article a characterization of the equipment is presented. In particular, the dependence of the quality of the signal on the amount of puffed gas as well as the influence of the puffed gas on the plasma discharge are assessed. A comparison has been performed between the use of hydrogen (which is the main discharge gas) and helium as the puffed gas showing that signals are much clearer when helium is used. Spectral and statistical properties of the signals are compared and the results are discussed.